Interchangeable lens video camera system

ABSTRACT

In an interchangeable lens assembly video camera system including an interchangeable lens assembly and a camera, a filter of an AF signal processing circuit ( 113 ) of the camera extracts a focus evaluation value signal from an image sensing signal corresponding to one or a plurality of focus detection areas in an image sensing surface, and on the basis of the transmitted focus evaluation value signal from the camera and data stored in a ROM ( 120 ), the microcomputer ( 116 ) performs a zooming operation of a zoom lens ( 102 ) while maintaining an in-focus state of a focus lens ( 105 ).

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a video camera system whose lensassemblies are interchangeable.

[0002] Conventionally, a so-called hill-climbing method is known as themethod of an automatic focusing device used in video apparatuses such asvideo cameras. The method performs focusing by extracting ahigh-frequency component from an image sensing signal obtained by animage sensing device such as a CCD and driving a taking lens such thatthe mountain-like characteristic curve of this high-frequency componentis a maximum.

[0003] This automatic focusing method requires neitheremission/reception of infrared rays nor special focusing optical membersfor detecting the movement of an image which changes in accordance withthe state of a focus. The method also has an advantage in that an objectcan be accurately focused regardless of whether the distance to theobject is long or short.

[0004] An example in which an automatic focusing method of he above sortis applied to an interchangeable lens video camera will be describedbelow with reference to FIG. 15.

[0005]FIG. 15 is a block diagram showing an interchangeable lens videocamera system as one prior art.

[0006] In FIG. 15, an automatic focusing system comprises a lensassembly 500 and a camera main body 550. Focusing is performed bydriving a focus lens 501 in the direction of an optical axis by a lensdriving motor 511. An image of light transmitting through this lens isformed on the image sensing surface of an image sensing device 502 andchanged into an electrical signal by photoelectric conversion. Thiselectrical signal is output as a video signal. The video signal issampled-and-held and amplified to a predetermined level by a CDS/AGC(Correlated Double Sampling/Auto Gain Control) circuit 503, andconverted into digital video data by an A/D (Analog/Digital) converter504. The data is input to a process circuit (not shown) of the cameraand converted into a standard television signal. The data is also inputto a bandpass filter (to be referred to as BPF hereinafter) 505.

[0007] The BPF 505 extracts a high-frequency component from the videosignal. A gate circuit 506 extracts only a signal corresponding to aportion set in an in-focus designated area in an image sensing surface.A peak hold circuit 507 holds peak values at intervals synchronized withintegral multiples of a vertical sync signal, generating an AF(AutoFocus) evaluation value.

[0008] An AF microcomputer 508 of the camera main body 550 fetches thisAF evaluation value and determines the driving velocity of a focus motor511 in accordance with an in-focus degree and the driving direction ofthe motor along which the AF evaluation value increases. The AFmicrocomputer 508 transmits the driving velocity and the drivingdirection of the focus motor 511 to a microcomputer 509 of the lensassembly 500.

[0009] In accordance with the designations from the AF microcomputer 508of the camera main body 550, the microcomputer 509 operates the focusmotor 511 via a motor driver 510 to drive the focus lens 501 in theoptical axis direction, thereby performing focusing.

[0010] In the above prior art, however, the camera main body has thefunction of controlling automatic focusing in order to allow aninterchange of lenses. Therefore, if, for example, the responsecharacteristics of automatic focusing are so determined as to be optimumfor a specific lens, the characteristics may not be optimum for otherlenses, resulting in a low versatility.

[0011] A problem arising when an interchangeable lens is a zoom lenswill be described below with reference to FIG. 16.

[0012]FIG. 16 is a block diagram of an interchangeable zoom lens videocamera system as another prior art.

[0013] In a conventional variable power lens assembly, a variable powerlens 21 and a compensating lens 22 are mechanically connected by a cam.When a zooming operation is manually or electrically performed, thevariable power lens 21 and the compensating lens 22 integrally move.

[0014] These variable power lens 21 and compensating lens 22 are calledzoom lenses. In this lens system, a lens (front lens) 1 which is closestto an object when the image is taken is a focus lens. The focus lens 1moves in the direction of an optical axis to perform focusing.

[0015] An image of light transmitting through these lenses is formed onthe image sensing surface of an image sensing device 3,photoelectrically converted into an electrical signal, and output as avideo signal. This video signal is sampled-and-held (correlated doublesampling) by a CDS/AGC circuit 4, amplified to a predetermined level byAGC (Auto Gain Control), and converted into digital video data by an A/Dconverter 5. The digital video data is input to a subsequent cameraprocess circuit (not shown) and converted into a standard televisionsignal. The data is also input to an AF signal processing circuit 6.

[0016] The AF signal processing circuit 6 extracts a high-frequencycomponent which changes in accordance with the focus state from thevideo signal. A microcomputer 7 for controlling the system fetches thishigh-frequency component as an AF evaluation value.

[0017] The microcomputer 7 determines the driving velocity of a focusmotor in accordance with the in-focus degree and the driving directionof the motor along which the AF evaluation value increases. Themicrocomputer 7 sends the velocity and the direction of the focus motorto a focus motor driver 9 of a lens assembly 12 and drives the focuslens 1 via a focus motor 10.

[0018] The microcomputer 7 also reads the state of a zoom switch 8 and,in accordance with the operation state of the zoom switch 8, determinesthe driving directions and the driving velocities of the zoom lenses 21and 22. The microcomputer 7 transmits these driving directions anddriving velocities to a zoom motor driver 11 of the lens assembly 12 anddrives the zoom lenses 21 and 22 via a zoom motor 12.

[0019] A camera main body 13 can be separated from the lens assembly 12and connected to another lens assembly. This widens the range ofshooting.

[0020] In recent integrated cameras for consumers having the abovestructure, the cam for mechanically connecting the compensating lenswith the variable power lens is no longer used in order to miniaturize acamera and enable shooting at a close distance such as when an object isalmost at the front surface of the lens. In these cameras, the locus ofmovement of the compensating lens is previously stored as lens cam datain a microcomputer, and the compensating lens is driven in accordancewith this lens cam data. Also, a focusing operation is performed byusing this compensating lens. Lenses of this type, i.e., so-called innerfocus type (rear focus type) lenses have become most popular.

[0021] According to the technical concept of the above prior art,however, all control operations are done in the camera main body, andthe lens assembly is driven in accordance with control signals suppliedfrom the camera main body. Therefore, to use an inner focus type lens asan interchangeable lens assembly, the camera main body must have thedata of the locus of movement of the focus lens, i.e., the lens camdata, for maintaining the in-focus state by compensating for a change inthe focal plane caused by a zooming operation.

[0022] This, however, imposes on the camera main body the serious burdenof having the lens cam data which differs from one lens assembly toanother. Accordingly, the method becomes unrealistic as the number ofinterchangeable lenses increases.

SUMMARY OF THE INVENTION

[0023] The present invention has been made in consideration of the abovesituation, and has as its object to provide an interchangeable lens(assembly) video camera system capable of performing optimum automaticfocusing with not only a front focus type lens assembly but also aninner focus type lens assembly.

[0024] A video camera system of the present invention and a camera and alens assembly constituting the system have the following characteristicfeatures.

[0025] There is provided a lens assembly which can be detachablyattached to a camera including focus detecting means, comprisingreceiving means for receiving a focus signal transmitted from thecamera, control means for checking an in-focus state on the basis of thefocus signal and determining a driving direction and a driving velocityof a focus lens of the lens assembly, and driving means for driving thefocus lens in accordance with the driving direction and the drivingvelocity.

[0026] There is also provided a camera to which a lens assembly can bedetachably attached, comprising extracting means for extracting a focussignal from an image sensing signal corresponding to an interior of oneor a plurality of focus detection areas in an image sensing surface ofthe camera, and transmitting means for transmitting the focus signal tothe lens assembly.

[0027] There is further provided a video camera system constituted bythe above lens assembly and camera.

[0028] There is further provided a lens assembly which can be detachablyattached to a camera including focus detecting means, comprisingreceiving means for receiving a focus signal and a state of a switch formanipulating a zooming operation, both of which are transmitted from thecamera, a zoom lens for performing a zooming operation, a focus lens formaintaining an in-focus state during the zooming operation, memory meansfor storing data representing a positional relationship between the zoomlens and the focus lens, zoom lens driving means for driving the zoomlens in accordance with the state of the switch, control means forchecking the in-focus state on the basis of the focus signal anddetermining a driving direction and a driving velocity of the focus lenswhile compensating for a movement of a focal plane caused by the zoomingoperation of the zoom lens on the basis of the data, and focus lensdriving means for driving the focus lens in accordance with the drivingdirection and the driving velocity.

[0029] There is further provided a camera to which a lens assembly canbe detachably attached, comprising extracting means for extracting afocus signal from an image sensing signal corresponding to an interiorof one or a plurality of focus detection areas in an image sensingsurface of the camera, a switch for manipulating a zooming operation ofa zoom lens of the lens assembly, and transmitting means fortransmitting the focus signal and a state of the switch to the lensassembly.

[0030] There is further provided a video camera system constituted bythe above lens assembly and camera, wherein the lens assembly controlsthe operation of the focus lens.

[0031] In any of the above constructions, the extracting means comprisesa plurality of filter means for extracting a signal of a predeterminedfrequency component as the focus signal from the image sensing signal.

[0032] The extracting means further comprises peak value detecting meansfor detecting a peak value of a luminance component in the image sensingsignal.

[0033] The extracting means further comprises contrast componentdetecting means for detecting a contrast component in the image sensingsignal.

[0034] The extracting means further comprises peak holding means fordetecting the contrast component by holding a peak value of a differencebetween a maximum value and a minimum value of the luminance component.

[0035] The camera may further comprise a switch for permitting anautomatic focusing operation, and the lens assembly may control thefocus lens when the switch permits the automatic focusing operation.

[0036] The camera may further comprise normalizing means for normalizingthe output from the extracting means and, when an image of a specificobject is taken, substantially the same focus signal may be output tothe lens assembly under the same taking conditions even if thecharacteristics of cameras vary.

[0037] Data representing the type of the focus signal may be transmittedbetween the camera and the lens assembly, and the control of the focuslens may be changed in accordance with the type signal.

[0038] Other features and advantages of the present invention will beapparent from the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

[0040]FIG. 1 is a block diagram of an interchangeable lens video camerasystem according to an embodiment of the present invention;

[0041]FIG. 2 is a block diagram showing an internal configuration of anAF signal processing circuit of the camera according to the embodimentof the present invention;

[0042]FIG. 3 is a view for explaining the operations and timings ofextraction of various focus evaluation values according to theembodiment of the present invention;

[0043]FIG. 4 is a flow chart of AF processing in the embodiment of thepresent invention;

[0044]FIG. 5 is a timing chart showing the timings of communications ofthe AF evaluation values to a lens assembly in the embodiment of thepresent invention;

[0045]FIG. 6 is an illustration showing the locus of movement (lens camdata) of a focus lens used to maintain an in-focus state by compensatingfor the position of a focal plane which changes with a zooming operationof a zoom lens in the embodiment of the present invention;

[0046]FIG. 7 is an illustration for explaining a method of calculating alocus not stored in the lens cam data from the information of aplurality of loci stored in the lens cam data in the embodiment of thepresent invention;

[0047]FIG. 8 is an illustration for explaining a method of calculating alocus not stored in the lens cam data from the information of aplurality of loci stored in the lens cam data in the embodiment of thepresent invention;

[0048]FIGS. 9A and 9B are illustrations for explaining an algorithm forallowing the focus lens to trace the locus stored in the lens cam datain the embodiment of the present invention;

[0049]FIGS. 10A and 10B are views showing details of the evaluationvalues and version information exchanged between the camera and the lensaccording to the first modification of the embodiment of the presentinvention;

[0050]FIG. 11 is a flow chart for explaining the processing performed bya microcomputer of a lens assembly according to the first modificationof the embodiment of the present invention;

[0051]FIG. 12 is a flow chart for explaining a method of matching theversions of communications between the camera and the lens assemblyaccording to the first modification of the embodiment of the presentinvention;

[0052]FIG. 13 is a block diagram of an interchangeable lens video camerasystem according to the second modification of the embodiment of thepresent invention;

[0053]FIGS. 14A to 14D are illustrations for explaining the processingdone by an evaluation value normalizing circuit 132 which constitutes anormalizing means in the embodiment of the present invention;

[0054]FIG. 15 is a block diagram showing the configuration of aninterchangeable lens video camera system as one prior art; and

[0055]FIG. 16 is a block diagram showing the configuration of aninterchangeable lens video camera system as another prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0056] A preferred embodiment of the present invention will be describedin detail in accordance with the accompanying drawings. FIG. 1 is ablock diagram of an interchangeable lens video camera system accordingto an embodiment of the present invention.

[0057] Referring to FIG. 1, a lens assembly 127 is detachably attachedto a main body 128 of the camera to constitute a so-calledinterchangeable lens system.

[0058] An image of light from an object is formed by image sensingdevices 106 to 108, e.g., CCDs, in the camera main body through a fixedfirst lens group 101, a second lens group 102 for performing a zoomingoperation, an iris stop 103, a fixed third lens group 104, and a fourthlens group 105 (to be referred to as a focus lens hereinafter) in thelens assembly 127. The fourth lens 105 has both a focusing function anda function of compensating for the movement of a focal plane caused byzooming.

[0059] The image pick devices 106, 107, and 108 in the camera main body128 are provided for three primary colors, red (R), green (G), and blue(B), respectively, constituting a so-called three-sensor image sensingsystem.

[0060] Images of the three primary colors, red, green, and blue, areformed on the image sensing devices 106, 107, and 108, respectively.

[0061] The images formed on the image sensing devices 106, 107, and 108are photoelectrically converted and amplified to their respectiveoptimum levels by amplifiers 109, 110, and 111, respectively. Theseimages are then input to a camera signal processing circuit 112 andconverted into a standard television signal. This signal is output to,e.g., a video recorder (not shown) and also input to an autofocus (AF)signal processing circuit 113.

[0062] An AF evaluation value generated by the AF signal processingcircuit 113 is read out at a period which is an integral multiple of avertical sync signal by a data read circuit 115 of a microcomputer 114in the camera main body 128. The readout AF evaluation value istransferred to a microcomputer 116 of the lens assembly 127 viacommunication interfaces 135 and 136.

[0063] In the camera signal processing circuit 112, the levels ofluminance signals of the output image sensing signals from the imagesensing devices are detected and transferred from the microcomputer 114to the microcomputer 116 of the lens assembly 127 via the communicationinterfaces 135 and 136. On the basis of this luminance signalinformation, an iris driver 124 is controlled, an IG (Iris Galvano)meter 123 is driven, and the iris stop 103 is controlled.

[0064] The aperture value of the iris stop 103 is detected by an encoder129, supplied to the microcomputer 116, and used as depth-of-fieldinformation.

[0065] The microcomputer 114 of the camera 128 transmits the states of azoom switch 130 and an AF switch 131 (when ON, an AF operation isperformed; when OFF, a manual focus mode is set) to the microcomputer116 of the lens via the communication interfaces 135 and 136.

[0066] In the microcomputer 116 of the lens, an AF arithmetic circuit117 receives the state of the AF switch 131 and the AF evaluation valuefrom the microcomputer 114 of the camera 128. When the AF switch 131 isON, the AF arithmetic circuit 117 operates a motor control circuit 118on the basis of the AF evaluation value, driving a focus motor 125 by afocus motor driver 126 and moving the focus lens 105 in the optical axisdirection to perform focusing.

[0067] The microcomputer 116 also receives the manipulated state of thezoom switch 130. In accordance with this manipulated state, themicrocomputer 116 controls a motor driver 122 to drive a zoom motor 121,driving the zoom lens 102 to perform a zooming operation.

[0068] The lens assembly is of an inner focus type, so the focal planemoves when the zoom lens 102 is driven. Therefore, the focus lens 105 isdriven in accordance with predetermined characteristics as the zoom lens102 is driven, thereby simultaneously performing an operation ofpreventing a blur (out of focus) caused by the displacement of the focalplane.

[0069] To perform this operation, lens cam data, i.e., a locusindicating a change in in-focus position of the focus lens with a changein the position of the zoom lens is stored in a ROM 120 of themicrocomputer 116 advance in accordance with the distance to an object.

[0070] Also, a zoom control circuit 119 reads out the locus (lens camdata) to be traced by the focus lens 105 during a zooming operation fromthe ROM 120 and thereby controls driving of the focus lens 104.

[0071] When the information from the microcomputer 114 of the cameramain body indicates that the AF switch 131 is OFF (manual focus mode)and the zoom switch 130 is depressed, the zoom control circuit 119specifies the in-focus locus along which the focus lens 105 is to traceduring a zooming operation and the trace direction, in accordance withthe information of the zoom direction operated by the zoom switch 130and with the position information obtained by detecting the positions ofthe zoom lens 102 and the focus lens 105 from the respective motordriving amounts or by using the encoder. The zoom control circuit 119reads out the specified locus and trace direction from the ROM 120 andcalculates the compensating velocity and direction of the focus lenscorresponding to the zooming operation.

[0072] The information of the compensating velocity and direction issupplied to the focus motor driver 126 to drive the focus motor 125.Consequently, the focus lens is driven to prevent a blur which occurswhen the focal point shifts during the zooming operation.

[0073] When the AF switch 131 is ON and the zoom switch 130 isdepressed, it is necessary to hold the in-focus state even if the objectmoves. Accordingly, the zoom control circuit 119 not only performscontrol on the basis of the lens cam data stored in the ROM 120 of themicrocomputer 116 as described above but also simultaneously refers tothe AF evaluation value signal sent from the microcomputer 114 of thecamera, thereby performing a zooming operation while holding theposition at which the AF evaluation value is a maximum.

[0074] That is, the driving velocity and the driving direction of thefocus lens 105 are calculated by adding the information of thecompensating velocity and direction of the focus lens obtained by thezoom control circuit 119 in accordance with the zooming operation to theinformation of the driving velocity and direction of the focus lensbased on the output focus movement information, obtained by AFprocessing, from the AF circuit 117. The driving velocity and directionthus calculated are supplied to the focus motor driver 126.

[0075] When the AF switch 131 is ON and the zoom switch 130 is notdepressed, the AF circuit 117 in the microcomputer 116 receives the AFevaluation value transmitted from the microcomputer 114 of the camera128. On the basis of this AF evaluation value, the motor control circuit118 is operated, the focus motor 125 is driven by the focus motor driver126, and focusing is performed by moving the focus lens 105 in theoptical axis direction so that the AF evaluation value is maximum.

[0076] The aperture value of the iris stop 103 is detected by theencoder 129, supplied to the microcomputer 116, and used as thedepth-of-field information to compensate for, e.g., the velocity of thefocus lens 105.

Autofocus Operation

[0077] The AF signal processing circuit 113 in the camera signalprocessing circuit 112 will be described below with reference to FIG. 2.FIG. 2 is a block diagram showing the internal configuration of the AFsignal processing circuit of the camera according to the embodiment ofthe present invention. Referring to FIG. 2, the image sensing deviceoutputs of red (R), green (G), and blue (B) are amplified to theirrespective optimum levels by amplifiers 109, 110, and 111 and suppliedto the AF signal processing circuit 113. The output signals areconverted into digital signals by A/D converters 206, 207, and 208 andsupplied to the camera signal processing circuit 112. At the same time,these digital signals are amplified to their respective optimum levelsby amplifiers 209, 210, and 211 and added by an adder 208, generating anautomatic focusing luminance signal S5.

[0078] The luminance signal S5 is input to a gamma circuit 213 andgamma-converted in accordance with a preset gamma curve, forming asignal S6 whose low-luminance component is increased and high-luminancecomponent is decreased. The gamma-converted signal S6 is applied to alow-pass filter (to be referred to as an LPF hereinafter) with a highcut-off frequency, i.e., a TE-LPF 214, and to an FE-LPF 215 which is anLPF with a low cut-off frequency. The TE-LPF 214 and the FE-LPF 215extract low-frequency components on the basis of the respective filtercharacteristics determined by the microcomputer 114 via a microcomputerinterface 253. Consequently, the TE-LPF 214 generates an output signalS7, and the FE-LPF 215 generates an output signal S8.

[0079] A line E/O signal is generated by the microcomputer 114 toidentify whether the horizontal line is an even-numbered line or anodd-numbered line. On the basis of this signal, the signals S7 and S8are switched by a switch 216 and applied to a high-pass filter (to bereferred to as an HPF hereinafter) 217.

[0080] That is, the signal S7 is supplied to the HPF 217 when thehorizontal line is an even-numbered line, and the signal S8 is suppliedto the HPF 217 when the horizontal line is an odd-numbered line.

[0081] The HPF 217 extracts only a high-frequency component inaccordance with filter characteristics determined for even- andodd-numbered lines by the microcomputer 114 via the microcomputerinterface 253. An absolute value circuit 218 obtains an absolute valueof the extracted signal to generate a positive signal S9. That is, thesignal S9 alternately indicates the levels of high-frequency componentsextracted by the filter having different filter characteristics foreven-and odd-numbered lines. Consequently, different frequencycomponents can be obtained by scanning one picture frame.

[0082] In accordance with an instruction supplied by the microcomputer114 via the microcomputer interface 253, a frame generating circuit 254generates gate signals L, C, and R for forming focus control gate framesL, C, and R, respectively, at positions in the image sensing surface asshown in FIG. 3.

[0083] Timings at which various kinds of information are fetched in theAF signal processing circuit 113 will be described below with referenceto FIG. 3 which shows the layout of focus detection areas in the imagesensing surface.

[0084]FIG. 3 is a view for explaining the operations and timings ofextraction of various focus evaluation values in the embodiment of thepresent invention. Referring to FIG. 3, the outside frame is aneffective image sensing surface of the outputs from the image sensingdevices 106, 107, and 108.

[0085] Three divided inside frames are focus detection gate frames. Aleft frame L, a central frame C, and a right frame R are formed inaccordance with the frame L generating gate signal, the frame Cgenerating gate signal, and the frame R generating gate signal,respectively, from the frame generating circuit 254.

[0086] At the start positions of these frames L, C, and R, reset signalsare output for the frames L, C, and R to generate initialization (reset)signals LR1, CR1, and RR1, respectively, thereby resetting integratingcircuits 232 to 237 and peak hold circuits 219 to 221, 225 to 227, and247 to 249.

[0087] Also, when the focus detection area consisting of the frames L,C, and R is completely scanned, a data transfer signal IR1 is generatedto transfer the integral values of the integrating circuits and the peakhold values of the peak hold circuits to their respective buffers.

[0088] Referring to FIG. 3, the scan of an even-numbered field isindicated by the solid lines, and the scan of an odd-numbered field isindicated by the dotted lines. In both the even- and odd-numberedfields, the TE-LPF output is selected on an even-numbered line, and theFE-LPF output is selected on an odd-numbered line.

[0089] Automatic focusing performed by the microcomputer by using aTE/FE peak evaluation value, a TE line peak integral evaluation value,an FE line peak integral evaluation value, a Y signal peak evaluationvalue, and a Max-Min evaluation value in each frame. Note that theseevaluations values are transmitted to the microcomputer 116 in the lensassembly and the microcomputer 116 performs actual control.

[0090] The signal S9 is supplied to the peak hold circuits 225, 226, and227 for detecting signal peak values in the left, central, and rightframes, i.e., the frames L, C, and R, in the image sensing surface.These peak hold circuits detect the peak values of high-frequencycomponents in their respective frames. The signal S9 is also supplied tothe line peak hold circuit 231 to detect the peak value of eachhorizontal line.

[0091] The peak hold circuit 225 receives the output gate signal L forforming the frame L from the frame generating circuit 254, the signalS9, and the Line E/O signal. As shown in FIG. 3, the peak hold circuit225 is initialized in the upper left corner, LR1, which is the startposition of the focusing frame L. The peak hold circuit 225 holds a peakvalue of the signal S9 in the frame L of either an even- or odd-numberedline designated by the microcomputer 114 via the microcomputer interface253. In the lower right corner IR1, i.e., when the entire focusing areais completely scanned, the peak hold value in the frame L is transferredto the area buffer 228 to generate a TE/FE peak evaluation value.

[0092] Likewise, the peak hold circuit 226 receives the output frame Csignal from the frame generating circuit 254, the Line E/O signal, andthe signal S9. As in FIG. 3, the peak hold circuit 226 is initialized inthe upper left corner, CR1, which is the start position of the focusingframe C. The peak hold circuit 226 holds a peak value of the signal S9in the frame C of either an even- or odd-numbered line designated by themicrocomputer 114 via the microcomputer interface 253. In IR1, i.e.,when the overall focusing area is completely scanned, the peak holdvalue in the frame C is transferred to the area buffer 229 to generate aTE/FE peak evaluation value.

[0093] Similarly, the peak hold circuit 227 receives the output frame Rsignal from the frame generating circuit 254, the Line E/O signal, andthe signal S9. As in FIG. 3, the peak hold circuit 227 is initialized inthe upper left corner, RR1, which is the start position of the focusingframe R. The peak hold circuit 227 holds a peak value of the signal S9in the frame R of either an even- or odd-numbered line designated by themicrocomputer 114 via the microcomputer interface 253. In IR1, i.e.,when the overall focusing area is completely scanned, the peak holdvalue in the frame R is transferred to the area buffer 230 to generate aTE/FE peak evaluation value.

[0094] The line peak hold circuit 231 receives the signal S9 and theoutput gate signals for generating the frames L, C, and R from the framegenerating circuit 254. The line peak hold circuit 231 is initialized atthe start point in the horizontal direction of each frame and holds apeak value of each line in the horizontal line of the signal S9 in eachframe.

[0095] The integrating circuits 232, 233, 234, 235, 236, and 237 receivethe output from the line peak hold circuit 231 and the Line E/O signalwhich identifies whether the horizontal line is an even- or odd-numberedline. The integrating circuits 232 and 235 receive the frame Lgenerating gate signal supplied from the frame generating circuit 254.The integrating circuits 233 and 236 receive the frame C generating gatesignal supplied from the frame generating circuit 254. The integratingcircuits 234 and 237 receive the frame R generating gate signal suppliedfrom the frame generating circuit 254.

[0096] The integrating circuit 232 is initialized in the upper leftcorner, LR1, which is the start position of the focusing frame L. Theintegrating circuit 232 adds the output from the line peak hold circuit231 to an internal register immediately before the end of aneven-numbered line in each frame. In IR1, the integrating circuit 232transfers the peak hold value to the area buffer 238 to generate a TEline peak integral evaluation value.

[0097] The integrating circuit 233 is initialized in the upper leftcorner, CR1, which is the start position of the focusing frame C. Theintegrating circuit 233 adds the output from the line peak hold circuit231 to an internal register immediately before the end of aneven-numbered line in each frame. In IR1, the integrating circuit 233transfers the peak hold value to the area buffer 239 to generate a TEline peak integral evaluation value.

[0098] The integrating circuit 234 is initialized in the upper leftcorner, RR1, which is the start position of the focusing frame R. Theintegrating circuit 234 adds the output from the line peak hold circuit231 to an internal register immediately before the end of aneven-numbered line in each frame. In IR1, the integrating circuit 234transfers the peak hold value to the area buffer 240 to generate a TEline peak integral evaluation value.

[0099] The integrating circuits 235, 236, and 237 perform the sameoperations as the integrating circuits 232, 233, and 234, respectively,except that the integrating circuits 235, 236, and 237 perform additionof odd-numbered line data, instead of performing addition ofeven-numbered line data such as done by the integrating circuits 232,233, and 234. The integrating circuits 235, 236, and 237 transfer theresults to the area buffers 241, 242, and 243, respectively, generatingFE line peak integral evaluation values.

[0100] The signal S7 is input to the peak hold circuits 219, 220, and221, a line maximum value hold circuit 244, and a line minimum valuehold circuit 245.

[0101] The peak hold circuit 219 receives the frame L generating gatesignal supplied from the frame generating circuit 254. The peak holdcircuit 219 is initialized in the upper left corner, LR1, which is thestart position of the frame L, and holds a peak value of the signal S7in each frame. In IR1, the peak hold circuit 219 transfers the peak holdresult to the buffer 222 to generate a peak evaluation value of aluminance level (to be referred to as a Y signal hereinafter).

[0102] Analogously, the peak hold circuit 220 receives the frame Cgenerating gate signal supplied from the frame generating circuit 254.The peak hold circuit 220 is initialized in the upper left corner, CR1,which is the start position of the frame C, and holds a peak value ofthe signal S7 in each frame. In IR1, the peak hold circuit 220 transfersthe peak hold result to the buffer 223 to generate a Y signal peakevaluation value.

[0103] Likewise, the peak hold circuit 221 receives the frame Rgenerating gate signal from the frame generating circuit 254. The peakhold circuit 221 is initialized in the upper left corner, RR1, which isthe start position of the frame R, and holds the peak value of thesignal S7 in each frame. In IR1, the peak hold circuit 221 transfers thepeak hold result to the buffer 224 to generate a Y signal peakevaluation value.

[0104] The line maximum value hold circuit 244 and the line minimumvalue hold circuit 245 receive the frame L, C, and R generating gatesignals supplied from the frame generating circuit 254. The line maximumvalue hold circuit 244 and the line minimum value hold circuit 245 areinitialized at the start point in the horizontal direction in each frameand hold the maximum value and the minimum value, respectively, of the Ysignal on one horizontal line of the signal S7 in each frame.

[0105] The maximum and the minimum values of the Y signal held by theline maximum value hold circuit 244 and the line minimum value holdcircuit 245 are input to a subtracter 246. The subtracter 246 calculatesa (maximum value-minimum value) signal, i.e., a signal S10 whichindicates the contrast, and inputs the signal to the peak hold circuits247, 248, and 249.

[0106] The peak hold circuit 247 is applied with the frame L generatinggate signal from the frame generating circuit 254. The peak hold circuit247 is initialized in the upper left corner, LR1, which is the startposition of the frame L, and holds a peak value of the signal S10 ineach frame. In IR1, the peak hold circuit 247 transfers the peak holdresult to the buffer 250 to generate a Max-Min evaluation value.

[0107] Similarly, the peak hold circuit 248 receives the frame Cgenerating gate signal from the frame generating circuit 254. The peakhold circuit 248 is initialized in the upper left corner, CR1, which isthe start position of the frame C, and holds a peak value of the signalS10 in each frame. In IR1, the peak hold circuit 248 transfers the peakhold result to the buffer 251 to generate a Max-Min evaluation value.

[0108] Analogously, the peak hold circuit 249 is applied with the frameR generating gate signal from the frame generating circuit 254. The peakhold circuit 249 is initialized in the upper left corner, RR1, which isthe start position of the frame R, and holds a peak value of the signalS10 in each frame. In IR1, the peak hold circuit 249 transfers the peakhold result to the buffer 252 to generate a Max-Min evaluation value.

[0109] In IR1, i.e., when the entire focusing area consisting of theframes L, C, and R is completely scanned, the data in these frames aretransferred to the buffers 222, 223, 224, 228, 229, 230, 238, 239, 240,241, 242, 243, 250, 251, and 252. Simultaneously, the frame generatingcircuit 254 sends an interrupt signal to the microcomputer 114 andtransfers the data, which are transferred to these buffers, to themicrocomputer 114.

[0110] That is, upon receiving the interrupt signal, the microcomputer114 reads out the data (focus evaluation values) from the buffers 222,223, 224, 228, 229, 230, 238, 239, 240, 241, 242, 243, 250, 251, and 252via the microcomputer interface 253 before the succeeding scan of theframes L, C, and R is completed and the data are transferred to thesebuffers. As will be described later, the microcomputer 114 transfers thedata to the microcomputer 116 in synchronism with a vertical syncsignal.

[0111] The microcomputer 116 of the lens assembly 127 detects the focusstate by performing calculations by using these transferred focusevaluation values. The microcomputer 116 then calculates, e.g., thedriving velocity and the driving direction of the focus motor 125 andcontrols driving of the focus motor 125, thereby driving the focusinglens 105.

[0112] The characteristics and applications of the above evaluationvalues will be described below.

[0113] The TE/FE peak evaluation value represents an in-focus degree andis a peak hold value. Therefore, this evaluation value is lessinfluenced by a camera shake and comparatively less depends upon thestate of an object. For these reasons, this evaluation value is optimumfor in-focus degree determination and reactivation determination.

[0114] The TE line peak integral evaluation value and the FE line peakintegral evaluation value also represent an in-focus degree. However,these evaluation values are optimum for direction determination sincethey have little noise and are stable as a result of integration. of theabove peak evaluation values and line peak integral evaluation values,each TE evaluation value is formed by extracting higher frequencies andhence is optimum as an evaluation value near the in-focus point. Incontrast, each FE evaluation value is optimum when an image is largelyblurred in a position very far from the in-focus point. Accordingly, byadding these signals or selectively switching the signals in accordancewith the TE level, it is possible to perform AF over a wide dynamicrange from the state in which an image is largely blurred to thevicinity of the in-focus point.

[0115] The Y signal peak evaluation value and the Max-Min evaluationvalue do not depend much upon the in-focus degree but upon the state ofan object. Therefore, these evaluation values are optimum to check thechange or movement of an object in order to reliably perform in-focusdegree determination, reactivation determination, and directiondetermination. These values are also used in normalization for removingthe influence of a change in brightness.

[0116] More specifically, the Y signal peak evaluation value is used tocheck whether the object is a high-luminance object or a low-luminanceobject. The Max-Min evaluation value is used to check whether thecontrast is high or low. Furthermore, optimum AF control can beperformed by predicting and compensating for the peak values, i.e., themagnitudes of peaks, on the characteristic curves of the TE/FE peakevaluation value, the TE line peak integral evaluation value, and the FEline peak integral evaluation value.

[0117] These evaluation values are transferred from the camera main body128 to the lens assembly 127 and supplied to the microcomputer 116 ofthe lens assembly 127, and the automatic focusing operation isperformed.

[0118] The algorithm of an automatic focusing operation performed by themicrocomputer 116 of the lens assembly 127 will be described below withreference to FIG. 4.

[0119]FIG. 4 is a flow chart of AF processing in this embodiment of thepresent invention.

[0120] When the processing is started, the microcomputer 116 activatesthe AF operation in step S1, and the flow advances to step S2. In stepS2, the microcomputer 116 checks the distance from the in-focus point bycomparing the level of the TE or FE peak with a predetermined threshold,and performs velocity control.

[0121] If the TE level is low, i.e., if the current focus point is farfrom the in-focus point and therefore the image is predicted to belargely blurred, the microcomputer 116 performs hill-climbing controlfor the focus lens by controlling the direction of the lens by primarilyusing the FE line peak integral evaluation value. When the TE levelrises to a certain degree near the peak of the characteristic curve, themicrocomputer 116 performs hill-climbing control for the focus lens byusing the TE line peak integral evaluation value. In this way, themicrocomputer 116 so performs control that the in-focus point can beaccurately detected.

[0122] If the lens comes close to the focus point, the flow advances tostep S3 and the microcomputer 116 determines the peak of thecharacteristic curve by using the absolute value of the TE or FE peakevaluation value or a change in the TE line peak integral evaluationvalue. If the microcomputer 116 determines that the level of theevaluation value is highest at the peak, i.e., the in-focus point, themicrocomputer 116 stops the focus lens in step S4 and advances toreactivation standby in step S5.

[0123] In the reactivation standby, if the microcomputer 116 detectsthat the level of the TE or FE peak evaluation value decreases by apredetermined level or more from the peak value obtained when thein-focus point is detected, the microcomputer 116 reactivates theoperation in step S6.

[0124] In the loop of the automatic focusing operation as describedabove, the velocity of the focus lens is controlled by using the TE/FEpeak. The level of the absolute value for determining the peak of thecharacteristic curve and the change in the TE line peak integralevaluation value are determined by predicting the height of the hill bychecking the object by using the Y peak evaluation value or the Max-Minevaluation value. The AF operation can always be performed by repeatingthe above processing.

[0125]FIG. 5 is a timing chart for explaining the timing at which themicrocomputer 114 of the camera main body 128 transmits various datasuch as the AF evaluation value to the microcomputer 116 of the lensassembly 127. As described previously, the timing of communicationbetween the camera main body 128 and the lens assembly 127 is such thatthe AF evaluation value read out by the microcomputer 114 is transferredto the microcomputer 116 immediately after the next vertical sync signalin synchronism with the vertical sync signal (V synchronization).

[0126] As a consequence, the AF operation can be controlled insynchronism with the vertical sync signal.

Zooming Operation

[0127] The relationship between the movements of the zoom lens 102 andthe focus compensating lens 105 and a method of referring to the AFevaluation value signal during a zooming operation from wide totelephoto will be described below.

[0128] In the lens system as illustrated in FIG. 1, the focus lens 105has both the compensating function and the focusing function.Accordingly, the position of the focus lens 105 for focusing an image onthe image sensing devices 106, 107, and 108 change in accordance withthe object distance even at the same focal length.

[0129]FIG. 6 shows the result of continuous plotting of the position ofthe focus lens 105 for focusing an image on the imaging plane of eachimage sensing device while the object distance is changed at differentfocal lengths. In FIG. 6, the abscissa indicates the position (focallength) of the zoom lens, and the ordinate indicates the position of thefocus lens. Each locus information represents the contents of the lenscam data of the ROM 120 of the microcomputer 116.

[0130] During the zooming operation, one of the loci shown in FIG. 6 isselected in accordance with the object distance, and the focus lens 105is moved to trace that locus. This allows a zooming operation free froma blur.

[0131] In a lens system by which focusing is performed by using a lens(front lens) closest to an object, a compensating lens is providedindependently of a variable power lens, and the variable power lens andthe compensating lens are coupled by a mechanical cam ring.

[0132] A manual zoom knob, for example, is formed on this cam ring, andthe focal length is manually changed. Even if the knob is moved as fastas possible, the cam ring rotates to trace the movement of the knob, andthe variable power lens and the compensating lens move along a camgroove of the cam ring. Therefore, no blur is caused by the aboveoperation as long as the focus lens is focused on an object.

[0133] In controlling the inner focus type lens system of thisembodiment having the characteristics as described above, however, whena zooming operation is performed while the in-focus state is held, it isnecessary to store the locus information (FIG. 6) as the lens cam datain the ROM 120 of the microcomputer 116, read out the locus informationfrom the ROM 120 in accordance with the position or the moving velocityof the zoom lens 102, and move the focus lens 105 on the basis of thereadout information.

[0134]FIG. 7 is a graph for explaining one invented locus tracingmethod. In FIG. 7, reference symbols Z0, Z1, Z2, . . . , Z6 denote thepositions of the zoom lens; and a0, a1, a2, . . . , a6 and b0, b1, b2, .. . , b6, representative loci stored as the lens cam data in the ROM 120of the microcomputer 116.

[0135] Also, p0, p1, p2, . . . , p6 denote loci calculated on the basisof the above two loci. This locus calculation is done by the followingequation:

p(n+1)=|p(n)−a(n)|/|b(n)−a(n)|*|b(n+1)−a(n+1)|+a(n+1)  (1)

[0136] In equation (1), if, for example, the focus lens is at p0 in FIG.7, the ratio at which p0 internally divides a line segment b0−a0 iscalculated, and the point at which a line segment b1−a1 is internallydivided by this ratio is given as p1.

[0137] The focus lens moving velocity for holding the in-focus state canbe known from this positional difference, p1−p0, and the time requiredfor the zoom lens to move from Z0 to Z1.

[0138] An operation when there is no such limitation that the stopposition of the zoom lens 102 must be on a boundary having thepreviously stored representative locus data will be described below.

[0139]FIG. 8 is a graph for explaining a method of calculating a locusnot stored on the basis of a plurality of pieces of stored locusinformation. FIG. 8 extracts a part of FIG. 7, and the zoom lens cantake any arbitrary position.

[0140] In FIGS. 7 and 8, the ordinate indicates the focus lens position,and the abscissa indicates the zoom lens position. The representativelocus positions (the focus lens positions with respect to the zoom lenspositions) stored as the lens cam data in the ROM 120 of themicrocomputer 116 are represented as follows for various objectdistances with respect to zoom lens positions Z0, Z1, . . . , Zk−1, Zk,. . . , Zn:

[0141] a0, a1, . . . , ak−1, ak, . . . , an

[0142] b0, b1, . . . , bk−1, bk, . . . , bn

[0143] If the zoom lens position is Zx not on a zoom boundary and thefocus lens position is Px, ax and bx are calculated as follows:

ax=ak−(Zk−Zx)*(ak−ak−1)/(Zk−Zk−1)  (2)

bx=bk−(Zk−Zx)*(bk−bk−1)/(Zk−Zk−1)  (3)

[0144] That is, ax and bx can be calculated by internally dividing datahaving the same object distance of the four stored representative locusdata (ak, ak−1, bk, and bk−1 in FIG. 8) by the internal ratio obtainedfrom the current zoom lens position and the two zoom boundary positions(e.g., Zk and zk−1 in FIG. 8) on the two sides of the current zoom lensposition.

[0145] In this case, pk and pk−1 can be calculated, as shown in equation(1), by internally dividing data having the same focal length of thefour stored representative data (ak, ak−1, bk, and bk−1 in FIG. 8) bythe internal ratio obtained from ax, px, and bx.

[0146] When zooming is performed from wide to telephoto, the focus lensmoving velocity for holding the in-focus state can be known from thepositional difference between the focus position pk to be traced and thecurrent focus position px and the time required for the zoom lens tomove from Zx to Zk.

[0147] When zooming is performed from telephoto to wide, the focus lensmoving velocity for holding the focused state can be known from thepositional difference between the focus position pk−1 to be traced andthe current focus position px and the time required for the zoom lens tomove firm Zx to Zk−1. The locus tracing method as described above isinvented.

[0148] When the AF switch 131 is ON, it is necessary to trace the locuswhile maintaining the in-focus state. When the zoom lens moves in adirection from telephoto to wide, the diverged loci converge as can beseen from FIG. 6. Therefore, the in-focus state can be maintained by theabove locus tracing method.

[0149] In a direction from wide to telephoto, however, a locus which thefocus lens in the point of convergence is to trace is unknown.Consequently, the in-focus state cannot be maintained by the locustracing method as above.

[0150]FIGS. 9A and 9B are graphs for explaining one locus tracing methodinvented to solve the above problem. In each of FIGS. 9A and 9B, theabscissa indicates the position of a zoom lens. In FIG. 9A, the ordinateindicates the level of a high-frequency component (sharpness signal) ofa video signal as an AF evaluation signal. In FIG. 9B, the ordinateindicates the position of a focus lens.

[0151] Assume that in FIG. 9B, a focusing locus is a locus 604 when azooming operation is performed for a certain object.

[0152] Assume also that a tracing velocity with respect to a locusindicated by lens cam data closer to a wide side than a zoom position606 (z14) is positive (the focus lens is moved to the closest focusingdistance), and that a tracing velocity with respect to a locus indicatedby lens cam data when the focus lens is moved in the direction ofinfinity on a telephoto side from the position 606 is negative.

[0153] When the focus lens traces the locus 604 while being kept in thein-focus state, the magnitude of the sharpness signal is as indicated by601 in FIG. 9A. It is generally known that a zoom lens kept in thein-focus state has an almost fixed sharpness signal level.

[0154] Assume that in FIG. 9B, a focus lens moving velocity for trackingthe focusing locus 604 during a zooming operation is Vf0. When an actualfocus lens moving velocity is vf and a zooming operation is performed byincreasing or decreasing Vf with respect to Vf0 for tracing the locus604, the resulting locus is zigzagged as indicated by reference numeral605.

[0155] Consequently, the sharpness signal level so changes as to formpeaks and valleys as indicated by reference numeral 603. The magnitudeof the level 603 is a maximum at positions where the loci 604 and 605intersect (at even-numbered points of Z0, Z1, . . . , Z16) and is aminimum at odd-numbered points where the moving direction vectors of thelocus 605 are switched.

[0156] Reference numeral 602 denotes a minimum value of the level 603.When a level TH1 of the value 602 is set and the moving directionvectors of the locus 605 are switched every time the magnitude of thelevel 603 equals the level TH1, the focus lens moving direction afterthe switching can be set in a direction in which the movement approachesthe in-focus locus 604.

[0157] That is, each time an image is blurred by the difference betweenthe sharpness signal levels 601 and 602 (TH1), the moving direction andvelocity of the focus lens are so controlled as to decrease the blur.Consequently, a zooming operation by which a degree (amount) of blur issuppressed can be performed.

[0158] The use of the above method is effective even in a zoomingoperation from wide to telephoto, as shown in FIG. 6, in which convergedloci diverge. That is, even if the in-focus velocity Vf0 is unknown, theswitching operation is repeated as indicated by 605 (in accordance witha change in the sharpness signal level) while the focus lens movingvelocity Vf is controlled with respect to the tracing velocity(calculated by using p(n+1) obtained from equation (1)) explained inFIG. 6. As a consequence, it is possible to select an in-focus locus bywhich the sharpness signal level is not decreased below the level 602(TH1), i.e., a predetermined amount or more of blur is not produced.

[0159] Assuming a positive compensating velocity is Vf+ and a negativecompensating velocity is Vf−, the focus lens moving velocity Vf isdetermined by

Vf=Vf0 +Vf+  (4)

Vf0 +Vf−  (5)

[0160] In order that no deviation is produced when the tracing locus isselected by the above method of zooming operation, the compensatingvelocities Vf+ and Vf− are so determined that the internal angle of thetwo vectors of Vf obtained by equations (4) and (5) is divided into twoequal parts.

[0161] Another method is proposed in which the increasing/decreasingperiod of the sharpness signal is changed by changing the compensatingamount by using the compensating velocity in accordance with the object,the focal length, or the depth of field, thereby improving the accuracyof the selection of the tracing locus.

[0162] In the embodiment as described above, the lens assembly includesthe focus lens locus information and the AF circuit, and a plurality ofevaluation values are transmitted from the camera main body to the lensassembly. Accordingly, the lens assembly can be informed of theoperation state of the focus lens, and this makes it possible to realizecomplicated control of the focus lens by using the lens assembly capableof a zooming operation. Consequently, a video camera system with whichvarious lens assemblies can be used is realized without complicating theconstruction of the camera main body.

First Modification of Embodiment

[0163] In this modification, evaluation values and version informationindicating the type and the contents of each evaluation value aretransferred from the camera 128 to the lens assembly 127 and supplied tothe microcomputer 116 to perform an automatic focusing operation. Therest of the configuration is identical with that of the above embodimentand so a detailed description thereof will be omitted.

[0164] The version information of the evaluation value will be describedbelow. This version information allows the selection of an optimumsignal as an AF evaluation value in accordance with the function andperformance of a camera main body. For example, when the sensitivity orthe number of pixels of the image sensing devices 106, 107, and 108 isgreatly increased compared to that of conventional devices andconsequently the frequency characteristics or the dynamic range of avideo signal is improved, it is predicted that the frequency componentof a signal indicating an in-focus degree shifts to higher frequenciesand a change in the evaluation value when the lens is defocused by aminimum diameter of a circle of confusion becomes larger.

[0165] Accordingly, it is necessary to change the filter characteristicsof the TE-LPF 214 and the FE-LPF 215 from the conventional settings, andthe obtained AF evaluation value becomes different from the conventionalevaluation value.

[0166] Assuming the former version of an evaluation value is Ver.1 andthe latter version is Ver.2, FIGS. 10A and 10B illustrate the detailedcontents of the versions and the evaluation values transmitted from thecamera main body to the lens assembly.

[0167] In this modification, it is assumed, for the sake of simplicity,that the type of evaluation value remains unchanged even when itsversion changes. However, the present invention is not limited to thismodification, provided that the lens assembly as the reception side cancontrol the number of words to be transmitted and the type or contentsof an evaluation value of each word.

[0168] As described above, the characteristic of an evaluation valuechanges in accordance with the version. Therefore, AF with higherperformance can be realized by making the AF control algorithm meet thecharacteristic.

[0169]FIG. 10A shows the AF evaluation values of the two versionstransmitted from the camera main body to the lens assembly. FIG. 10Bshows the contents transmitted from the lens assembly to the camera mainbody.

[0170] The algorithm of an automatic focusing operation performed by themicrocomputer 116 of the lens assembly will be described below withreference to FIG. 11.

[0171] In this modification, the microcomputer 116 corresponds to AFcontrol of Ver.2. The camera main body corresponds to both Ver.1 andVer.2.

[0172]FIG. 11 is a flow chart showing a focusing operation performed bythe lens assembly in the first modification of the embodiment of thepresent invention.

[0173] The microcomputer 116 activates the system in step S101 andchecks the version of an evaluation value in step S102. If the versionis Ver.1, the microcomputer 116 executes hill-climbing control 1 in stepS103. If the version is Ver.2, the microcomputer 116 executeshill-climbing control 2 in step S104. If the level of the TE or FE peakis low, the microcomputer 116 determines that the focus lens is far fromthe in-focus point and drives the focus lens at a high velocity(velocity control). The microcomputer 116 controls the search for thein-focus point by performing direction control by primarily using the TEline peak integral evaluation value near the in-focus point and the FEline peak evaluation value if the lens is far from the in-focus point.

[0174] Assuming, as described above, that an evaluation value of Ver.2corresponds to a video signal obtained from a high-resolution,high-sensitivity image sensing device, in the vicinity of the in-focuspoint, the image is blurred more by an evaluation value of Ver.2 thanthat of Ver.1 when the focus lens is moved the same amount.

[0175] Accordingly, the lens moving velocity near the in-focus point instep 104 is set to be lower than that in step S103 (S103: velocity α,S104: velocity β=a/2).

[0176] In step S105, the microcomputer 116 determines the peak of thecharacteristic curve (the in-focus point) from the absolute value of theTE or FE peak evaluation value and a change in the TE line peak integralevaluation value. The microcomputer 116 stops the lens at a point atwhich the level is highest, and stores these evaluation values in thememory.

[0177] In step S106, the microcomputer 116 performs the same processingas in step S102. If the version of an evaluation value is Ver.1, theflow advances to reactivation standby 1 in step S107. If the version isVer.2, the flow advances to reactivation standby 2 in step S108.

[0178] In the reactivation standby, the microcomputer 116 detectswhether the level of the TE or FE peak evaluation value decreases fromthe level stored in the memory in step S105. If the decrease isdetected, the flow advances to step S109 to perform reactivation.

[0179] If an evaluation value of Ver.2 corresponds to a high-resolution,high-sensitivity image sensing signal, the level of an evaluation valueof Ver.2 tends to change more than that of Ver.1 for visually the sameblur. Therefore, the evaluation value variation threshold fordetermining reactivation in reactivation standby 2 in step S108 is setto be larger than that in step S107 (in this modification, reactivationis performed when the level changes 20% or more from the stored level instep S107 and when the level changes 40% or more from the stored levelin step S108).

[0180] In the loop of the automatic focusing operation as describedabove, the velocity control of the focus lens is performed by using theTE/FE peak. A characteristic curve is predicted by checking the objectby using the Y peak evaluation value or the Max-Min evaluation value,and the absolute value for determining the peak of the characteristiccurve and the change in the TE line peak integral evaluation value aredetermined on the basis of the characteristic curve.

[0181] In the above explanation, it is assumed that the version of thelens assembly is Ver.2. If the lens assembly is Ver.1, it is onlynecessary to perform the processing in the order of steps S101, S103,S105, S106, S107, and S109 in FIG. 11.

[0182] The communication timings between the camera main body and thelens will be described below with reference to FIG. 5. As describedabove, the AF evaluation values read out by the microcomputer of themain body are transferred to the microcomputer of the lens immediatelyafter the next vertical sync signal in synchronism with the verticalsync signal (V synchronization).

[0183]FIG. 12 is a flow chart for explaining the method of matching theversions of communications between the camera main body and the lens.This flow chart shows the processing performed by the microcomputer 114of the camera main body. In FIG. 12, it is assumed that the camera mainbody corresponds to the evaluation values of Ver.2 in FIG. 10A and thelens assembly corresponds to both the AF control versions Ver.1 andVer.2 in FIG. 10B.

[0184] In step S111, the microcomputer 114 activates the system. In stepS112, the microcomputer 114 performs initialization, i.e., performssettings for generating AF evaluation values corresponding to the latestversion (in this case Ver.2) of the microcomputer of the main body (inthe case explained in FIG. 11, the microcomputer 114 sets the filtercharacteristics of the TE-LPF 214 and the FE-LPF 215 so that higherfrequencies than that in conventional methods can be extracted).

[0185] To communicate with the microcomputer 116 at the communicationtimings shown in FIG. 5, the microcomputer 114 waits in step S113 untilthe vertical sync signal comes. In step S114, the microcomputer 114performs mutual communication, i.e., exchanges data as illustrated inFIGS. 4A and 4B.

[0186] In step S115, the microcomputer 114 checks whether the version ofthe transmitted evaluation value agrees with the control version bywhich the microcomputer of the lens can perform AF control.

[0187] If the versions agree, the flow advances to step S118, and themicrocomputer 114 executes usual control of the camera, which includesAE (Automatic Exposure) control, AWB (Automatic White Balance) control,and the other processing to sense an image. The microcomputer 114 thenwaits in step S113 until the next vertical sync signal comes.

[0188] If the versions disagree in step S115, the flow advances to stepS116, and the microcomputer 114 performs settings for generating AFevaluation values corresponding to the AF control version of the lensassembly. The microcomputer 114 changes the version of the evaluationvalue in step S117, and the flow returns to step S113.

[0189] In this modification as described above, upgrading is realized bytransferring the type information of a focus signal. For example, afocus signal newly required in accordance with the progress oftechnologies such as a high-pixel CCD can be added to the conventionalfocus signal, or the contents or type of the signal can be changed. Itis also possible to provide a highly expandable video system byoptimizing AF control in accordance with the version of the transferredfocus signal.

Second Modification of Embodiment

[0190] The second modification of the embodiment of the presentinvention will be described below. FIG. 13 is a block diagram showingthe configuration of an interchangeable lens video camera system of thismodification. FIG. 13 differs from the video system in FIG. 1 in that amicrocomputer 114A incorporates an evaluation value normalizing circuit132. The rest of the configuration including the microcomputer 114A isidentical with the above embodiment (the same reference numerals as inFIG. 1 denote parts having the same functions in FIG. 13) and a detaileddescription thereof will be omitted.

[0191] In this modification, an AF evaluation value generated by the AFsignal processing circuit 113 is read out at a period which is anintegral multiple of a vertical sync signal by the data read circuit 115of the microcomputer 114A of the camera main body. The readoutevaluation value is normalized by the evaluation value normalizingcircuit 132 and transferred to the microcomputer 116 of the lensassembly.

[0192] The evaluation value normalizing circuit 132 will be describedbelow with reference to FIGS. 14A to 14D. FIGS. 14A to 14D are graphsshowing changes in the TE peak evaluation value when the lens issearched from the closest focusing distance to infinity while a certainobject is imaged.

[0193]FIGS. 14A and 14C show the values read out by the data readcircuits 115 of different cameras (image sensing means) when an image ofthe same object is taken by the same lens.

[0194] These output levels are different although an image of the sameobject is taken by the same lens. The evaluation value normalizingcircuit 132 determines levels such that the signal levels at two pointsP1 and P2 have predetermined values and, in accordance with the levelsthus determined, shifts, compresses, or expands the whole signal level.

[0195] The output from the evaluation value normalizing circuit 132 inFIG. 14A is shown in FIG. 14B, and the output from the evaluation valuenormalizing circuit 132 in FIG. 14C is shown in FIG. 14D. Although theinput levels to the evaluation value normalizing circuits 132 shown inFIGS. 14A and 14C are different, the output levels in FIGS. 14B and 14Dare almost the same. The evaluation value normalizing circuit 132performs similar normalization for other evaluation values.

[0196] That is, the evaluation value normalizing circuit 132 receivesthe TE peak values in the frames L, C, and R output from the buffers 228to 230, the TE peak integral values and the FE peak integral values inthe frames L, C, and R output from the buffers 238 to 243, and thecontrast peak values in the frames L, C, and R output from the buffers250 to 252. The evaluation value normalizing circuit 132 performsmaximum value level shift processing and minimum value level shiftprocessing for these input values. In the maximum value level shiftprocessing, the peak value of each input signal level is compressed orexpanded and forcibly matched with the level of P1 in FIGS. 14B and 14D.In the minimum value level shift processing, the minimum value of eachinput signal level is compressed or expanded and forcibly matched withthe level of P2 in FIGS. 14B and 14D. Although FIGS. 14A to 14Dillustrate the TE peak, other evaluation values described previously aresimilarly normalized and transmitted to the microcomputer 116 of thelens assembly 127.

[0197] Consequently, even if variations are present in the image sensingdevices 106 to 108 or the AF signal processing circuit 113 of the cameramain body, each focus evaluation value has a normalized predeterminedcharacteristic. Accordingly, even when a plurality of camera main bodieshaving different image sensing means are combined with different lensassemblies, a common output can be transferred to these lens assembliesby normalizing the focus signal. Additionally, since the respectiveoptimum response characteristics can be determined in the individuallens assemblies, objects to be imaged can be focused more stably in ataking area under various taking conditions.

[0198] As many apparently widely different embodiments of the presentinvention can be made without departing from the spirit and scopethereof, it is to be understood that the invention is not limited to thespecific embodiments thereof except as defined in the appended claims.

What is claimed is:
 1. An interchangeable lens assembly video camerasystem comprising a camera and an interchangeable lens assembly, whereinsaid camera comprises extracting means for extracting a focus signalfrom an image sensing signal corresponding to an interior of one or aplurality of focus detection areas in an image sensing surface of saidcamera, and transmitting means for transmitting the focus signal to saidlens assembly; said lens assembly comprises receiving means forreceiving the focus signal from said camera, control means fordetermining a driving direction and a driving velocity of a focus lensof said lens assembly, on the basis of the received focus signal, inorder to drive said focus lens to an in-focus point, and driving meansfor driving said focus lens in accordance with the driving direction andthe driving velocity; and said lens assembly controls an operation ofsaid focus lens.
 2. The system according to claim 1 , wherein saidextracting means comprises a plurality of filter means for extracting asignal of a predetermined frequency component as the focus signal fromthe image sensing signal.
 3. The system according to claim 2 , whereinsaid extracting means further comprises peak value detecting means fordetecting a peak value of a luminance component in the image sensingsignal.
 4. The system according to claim 2 , wherein said extractingmeans further comprises contrast component detecting means for detectinga contrast component in the image sensing signal.
 5. The systemaccording to claim 4 , wherein said extracting means further comprisespeak holding means for detecting the contrast component by holding apeak value of a difference between a maximum value and a minimum valueof the luminance component.
 6. A lens assembly which can be detachablyattached to a camera including focus detecting means, comprising:receiving means for receiving a focus signal transmitted from saidcamera; control means for checking an in-focus state on the basis of thefocus signal and determining a driving direction and a driving velocityof a focus lens of said lens assembly; and driving means for drivingsaid focus lens in accordance with the driving direction and the drivingvelocity.
 7. A camera to which a lens assembly can be detachablyattached, comprising: extracting means for extracting a focus signalfrom an image sensing signal corresponding to an interior of one or aplurality of focus detection areas in an image sensing surface of saidcamera; and transmitting means for transmitting the focus signal to saidlens assembly.
 8. The camera according to claim 7 , wherein saidextracting means comprises a plurality of filter means for extracting asignal of a predetermined frequency component as the focus signal fromthe image sensing signal.
 9. The camera according to claim 8 , whereinsaid extracting means further comprises peak value detecting means fordetecting a peak value of a luminance component in the image sensingsignal.
 10. The camera according to claim 8 , wherein said extractingmeans further comprises contrast component detecting means for detectinga contrast component in the image sensing signal.
 11. The cameraaccording to claim 10 , wherein said extracting means further comprisespeak holding means for detecting the contrast component by holding apeak value of a difference between a maximum value and a minimum valueof the luminance component.
 12. An interchangeable lens assembly videocamera system comprising a camera and an interchangeable lens assembly,wherein said camera comprises extracting means for extracting a focussignal from an image sensing signal corresponding to an interior of oneor a plurality of focus detection areas in an image sensing surface ofsaid camera, a switch for manipulating a zooming operation, andtransmitting means for transmitting the focus signal and a state of saidswitch to said lens assembly; said lens assembly comprises receivingmeans for receiving the focus signal and the state of said switch fromsaid camera, a zoom lens for performing a zooming operation; a focuslens for maintaining an in-focus state during the zooming operation,memory means for storing data representing a positional relationshipbetween said zoom lens and said focus lens, zoom lens driving means fordriving said zoom lens in accordance with the state of said switch,control means for checking the in-focus state on the basis of the focussignal and determining a driving direction and a driving velocity ofsaid focus lens while compensating for a movement of a focal planecaused by the zooming operation of said zoom lens on the basis of thedata, and focus lens driving means for driving said focus lens inaccordance with the driving direction and the driving velocity; and saidlens assembly controls operations of said focus lens and said zoom lens.13. The system according to claim 12 , wherein said extracting meanscomprises a plurality of filter means for extracting a signal of apredetermined frequency component as the focus signal from the imagesensing signal.
 14. The system according to claim 13 , wherein saidextracting means further comprises peak value detecting means fordetecting a peak value of a luminance component in the image sensingsignal.
 15. The system according to claim 13 , wherein said extractingmeans further comprises contrast component detecting means for detectinga contrast component in the image sensing signal.
 16. The systemaccording to claim 15 , wherein said extracting means further comprisespeak holding means for detecting the contrast component by holding apeak value of a difference between a maximum value and a minimum valueof the luminance component.
 17. A lens assembly which can be detachablyattached to a camera including focus detecting means, comprising:receiving means for receiving a focus signal and a state of a switch formanipulating a zooming operation, both of which are transmitted fromsaid camera; a zoom lens for performing a zooming operation; a focuslens for maintaining an in-focus state during the zooming operation;memory means for storing data representing a positional relationshipbetween said zoom lens and said focus lens; zoom lens driving means fordriving said zoom lens in accordance with the state of said switch;control means for checking the in-focus state on the basis of the focussignal and determining a driving direction and a driving velocity ofsaid focus lens while compensating for a movement of a focal planecaused by the zooming operation of said zoom lens on the basis of thedata; and focus lens driving means for driving said focus lens inaccordance with the driving direction and the driving velocity.
 18. Acamera to which a lens assembly can be detachably attached, comprising:extracting means for extracting a focus signal from an image sensingsignal corresponding to an interior of one or a plurality of focusdetection areas in an image sensing surface of said camera; a switch formanipulating a zooming operation of a zoom lens of said lens assembly;and transmitting means for transmitting the focus signal and a state ofsaid switch to said lens assembly.
 19. The camera according to claim 18, wherein said extracting means comprises a plurality of filter meansfor extracting a signal of a predetermined frequency component as thefocus signal from the image sensing signal.
 20. The camera according toclaim 19 , wherein said extracting means further comprises peak valuedetecting means for detecting a peak value of a luminance component inthe image sensing signal.
 21. The camera according to claim 19 , whereinsaid extracting means further comprises contrast component detectingmeans for detecting a contrast component in the image sensing signal.22. The camera according to claim 21 , wherein said extracting meansfurther comprises peak holding means for detecting the contrastcomponent by holding a peak value of a difference between a maximumvalue and a minimum value of the luminance component.
 23. Aninterchangeable lens assembly video camera system comprising a cameraand an interchangeable lens assembly, wherein said camera comprisesextracting means for extracting a focus signal from an image sensingsignal corresponding to an interior of one or a plurality of focusdetection areas in an image plane of said camera, a switch forpermitting an automatic focusing operation; and transmitting means fortransmitting the focus signal and a state of said switch to said lensassembly; said lens assembly comprises receiving means for receiving thefocus signal and the state of said switch from said camera, controlmeans for determining a driving direction and a driving velocity of afocus lens of said lens assembly on the basis of the received focussignal, when said switch permits the automatic focusing operation, inorder to drive said focus lens to an in-focus point, and driving meansfor driving said focus lens in accordance with the driving direction andthe driving velocity; and said lens assembly controls an operation ofsaid focus lens.
 24. The system according to claim 23 , wherein saidextracting means comprises a plurality of filter means for extracting asignal of a predetermined frequency component as the focus signal fromthe image sensing signal.
 25. The system according to claim 24 , whereinsaid extracting means further comprises peak value detecting means fordetecting a peak value of a luminance component in the image sensingsignal.
 26. The system according to claim 24 , wherein said extractingmeans further comprises contrast component detecting means for detectinga contrast component in the image sensing signal.
 27. The systemaccording to claim 26 , wherein said extracting means further comprisespeak holding means for detecting the contrast component by holding apeak value of a difference between a maximum value and a minimum valueof the luminance component.
 28. An interchangeable lens assembly videocamera system comprising a camera and an interchangeable lens assembly,wherein said camera comprises extracting means for extracting a focussignal from an image sensing signal corresponding to an interior of oneor a plurality of focus detection areas in an image sensing surface ofsaid camera, normalizing means for normalizing an output from saidextracting means, and transmitting means for transmitting the focussignal normalized by said normalizing means to said lens assembly; saidlens assembly comprises receiving means for receiving the normalizedfocus signal from said camera, control means for determining a drivingdirection and a driving velocity of a focus lens of said lens assemblyon the basis of the received focus signal, in order to drive said focuslens to a focus point, and driving means for driving said focus lens inaccordance with the driving direction and the driving velocity; and saidlens assembly controls an operation of said focus lens.
 29. The systemaccording to claim 28 , wherein said extracting means comprises aplurality of filter means for extracting a signal of a predeterminedfrequency component as the focus signal from the image sensing signaland, when an image of a specific object is taken, said normalizing meansso performs normalization that the predetermined frequency component hassubstantially the same characteristics.
 30. The system according toclaim 29 , wherein said extracting means further comprises peak valuedetecting means for detecting a peak value of a luminance component inthe image sensing signal and, when an image of a specific object istaken, said normalizing means so performs normalization that the peakvalue has substantially the same value.
 31. The system according toclaim 29 , wherein said extracting means further comprises contrastcomponent detecting means for detecting a contrast component in theimage sensing signal and, when an image of a specific object is taken,said normalizing means so performs normalization that the contrastcomponent has substantially the same value.
 32. The system according toclaim 31 , wherein said extracting means further comprises peak holdingmeans for detecting the contrast component by holding a peak value of adifference between a maximum value and a minimum value of the luminancecomponent.
 33. A camera to which a lens assembly can be detachablyattached, comprising: extracting means for extracting a focus signalfrom an image sensing signal corresponding to an interior of one or aplurality of focus detection areas in an image sensing surface of saidcamera; normalizing means for normalizing an output from said extractingmeans; and transmitting means for transmitting the focus signalnormalized by said normalizing means to said lens assembly.
 34. Thecamera according to claim 33 , wherein said extracting means comprises aplurality of filter means for extracting a signal of a predeterminedfrequency component as the focus signal from the image sensing signaland, when an image of a specific object is taken, said normalizing meansso performs normalization that the predetermined frequency component hassubstantially the same characteristics.
 35. The camera according toclaim 34 , wherein said extracting means further comprises peak valuedetecting means for detecting a peak value of a luminance component inthe image sensing signal and, when an image of a specific object istaken, said normalizing means so performs normalization that the peakvalue has substantially the same value.
 36. The camera according toclaim 34 , wherein said extracting means further comprises contrastcomponent detecting means for detecting a contrast component in theimage sensing signal and, when an image of a specific object is taken,said normalizing means so performs normalization that the contrastcomponent has substantially the same value.
 37. The camera according toclaim 36 , wherein said extracting means further comprises peak holdingmeans for detecting the contrast component by holding a peak value of adifference between a maximum value and a minimum value of the luminancecomponent.
 38. An interchangeable lens assembly video camera systemcomprising a camera and an interchangeable lens assembly, wherein saidcamera comprises extracting means for extracting a focus signal from animage sensing signal corresponding to an interior of one or a pluralityof focus detection areas in an image sensing surface of said camera, andtransmitting means for transmitting the focus signal and datarepresenting a type of the focus signal to said lens assembly; said lensassembly comprises receiving means for receiving the focus signal andthe data representing the type of the focus signal from said camera,control means for determining a driving direction and a driving velocityof a focus lens of said lens assembly on the basis of the received focussignal and data representing the type of the focus signal, in order todrive said focus lens to an in-focus point, and driving means fordriving said focus lens in accordance with the driving direction and thedriving velocity; and said lens assembly controls an operation of saidfocus lens.
 39. The system according to claim 38 , wherein said controlmeans changes the control of the focusing operation in accordance withthe data representing the type information of the focus signal.
 40. Alens assembly which can be detachably attached to a camera includingfocus detecting means, comprising: receiving means for receiving a focussignal and data representing a type of the focus signal transmitted fromsaid camera; control means for checking an in-focus state on the basisof the focus signal and the data representing the type of the focussignal and determining a driving direction and a driving velocity of afocus lens of said lens assembly; and driving means for driving saidfocus lens in accordance with the driving direction. and the drivingvelocity.
 41. The lens assembly according to claim 40 , wherein saidcontrol means changes the method of controlling the focusing operationin accordance with the type information of the focus signal.
 42. Acamera to which a lens assembly can be detachably attached, comprising:extracting means for extracting a focus signal from an image sensingsignal corresponding to an interior of one or a plurality of focusdetection areas in an image sensing surface of said camera; andtransmitting means for transmitting the focus signal and datarepresenting a type of the focus signal to said lens assembly.